1. Field of the Invention
The present invention relates to a high-frequency package sealing a high-frequency element (e.g., semiconductor element) that operates in a high-frequency region and, particularly, in a millimeter wave region. More specifically, the invention relates to a high-frequency package that can be directly connected to a waveguide that is connected to an external electric circuit board (mother board) and that is capable of transmitting high-frequency signals with a low loss.
2. Description of the Prior Art
In an information-oriented society in recent years, information is transmitted in a wireless manner and on a personal basis as represented by a portable telephone. Under such circumstances, semiconductor elements that operate in a millimeter wave region (30 to 300 GHz) have been developed in order to transmit information at high speeds and in large quantities. Accompanying the progress in the high-frequency semiconductor element technology in recent years, a variety of applied systems have been proposed using electromagnetic waves in a millimeter wave region, such as a distance-between-the-cars radar and a wireless LAN. For example, there have been proposed a distance-between-the-cars radar using millimeter waves (see SC-7-6, Convention of Electronics Society, Japanese Academy of Electronic Information Communications, 1995), a cordless camera system (see C-137, Convention of Electronics Society, Japanese Academy of Electronic Information Communications, 1995), a high-speed wireless LAN (see C-139, Convention of Electronics Society, Japanese Academy of Electronic Information Communications, 1995).
Accompanying the application of millimeter waves, fabrication technology has also been improved to apply such waves. In dealing with a variety of electronic parts, in particular, a problem is how to decrease the size and cost while maintaining the required transmission characteristics.
Among the fabrication technologies, a serious problem remains in regard to a package containing a high-frequency element and a waveguide so that it is connected to an external electric circuit simply and with a small size. In particular, a problem is how to connect a package mounting a high-frequency element to an external electric circuit having a waveguide with the smallest transmission loss.
A conventional high-frequency package can be connected to a waveguide connected to an external electric circuit by a method in which a transmission passage formed in a high-frequency package is converted into a coaxial line by a connector, or a method in which the waveguide is connected to a microstrip line which is then connected to a transmission passage in the high-frequency package.
In recent years, there has been proposed a method in which a package containing a high-frequency element is directly connected to a waveguide in the external electric circuit (see SC-7-5, Convention of Electronics Society, Japanese Academy of Electronic Information Communications, 1995). According to this proposal, quartz is deposited to hermetically seal the element in a cavity, and the electromagnetic waves are introduced into the cavity through an area where quartz is deposited, to accomplish the connection to a waveguide-microstrip line converter board installed in the cavity.
According to the method of connecting the waveguide to the package through another transmission line such as a microstrip line or a connector, however, the structure of the connection becomes complex and, besides, a region must be maintained for forming a connector or other transmission line, causing the structure of the connection to become bulky. Moreover, the transmission loss may increase through the other line or connector.
On the other hand, the method of directly introducing the electromagnetic waves from the waveguide into the cavity in the package is effective in decreasing the size of the structure for connection. In order to decrease the loss of electromagnetic waves that pass through the member for forming a cavity (such as a closure), however, the portion for passage must be formed of a material having a small dielectric constant and a small loss tangent. For this purpose, a material having a low dielectric constant and a small loss, such as quartz, must be enclosed. However, the enclosing treatment not only loses reliability in the hermetic sealing but also is not quite suited for mass-production.
All of the cavity-forming member can be formed of a material having a low dielectric constant and a small loss. In fact, however, the material for constituting the package requires a variety of properties such as mechanical strength, air-tightness and metallizing property in addition to electric properties. There is available no suitable material that satisfies all of these properties and that can be cheaply obtained.
That is, the above-mentioned difficulty stems from the introduction of the high-frequency signals in the form of electromagnetic waves into the cavity of the package through the waveguide. That is, the signals are in the form of electromagnetic waves at a portion where they are introduced into the cavity, and it becomes necessary to accomplish both air-tight sealing and low loss in this portion.